Conventional articles of footwear include two primary elements, an upper and a sole structure. The upper provides a covering for at least a portion of the foot that comfortably receives and securely positions the foot with respect to the sole structure.
The sole structure is secured to a lower portion of the upper and is generally positioned between the foot and the ground. In addition to attenuating ground reaction forces, the sole structure may provide traction, control foot motions (e.g., by resisting over pronation), and impart stability, for example. Accordingly, the upper and the sole structure operate cooperatively to provide a comfortable structure that is suited for a wide variety of ambulatory activities, including walking and running.
The upper is often secured (e.g., by adhesives or stitching) to the sole structure to form a void for receiving the foot. A variety of material may be utilized for the upper, including leather, synthetic leather, and various textiles. A foam material may be located on the interior of the upper to enhance the comfort of the upper, and moisture-wicking textiles may be positioned adjacent the foot to limit the quantity of perspiration within the upper.
In open heel footwear, such as a sandal and clog, the upper generally covers at least a portion of a forward area of the foot and leaves a heel area of the foot exposed. More particularly, the upper of a sandal exposes at least a portion of the toes, whereas the upper of a clog covers substantially all of the forward area of the foot. In both a sandal and a clog, the heel area of the upper is generally left open, which allows the foot to enter and exit the footwear in a relatively easy manner.
In either a sandal or a clog, sole structure may be a single foam element, or the sole structure may have a foam midsole layer and a rubber outsole layer, for example. The sole structure may also include a sockliner, which is a thin, cushioning member located adjacent to a plantar (i.e., lower) surface of the foot to enhance footwear comfort. Although the sole structure is generally secured to the upper in a permanent manner, some articles of footwear with the open heel configuration may incorporate removable or interchangeable sole structure elements.